Fatal Flaw
by SavSilvy
Summary: Grieving may be a long and painful process but in time most people do recover. For Hiro Hamada though something probably went wrong along the way because from what Aunt Cass could see, he was moving on yet at the same time, he wasn't.


**Hi guys! I've been a lurker in the Big Hero Six fandom lately and I am so happy to know that there are so much great fanfics to read here. I don't know if I'll be able to contribute fanfics as great as the better ones in this fandom but I might as well try. This one is a fic I wanted to write for a while.**

 **It is set a few years after the movie and you will probably understand the timeline as I go along with it.**

 **It will delve into the workings of Hiro's inner mind as he deals with Tadashi's death even years after. There will be more themes later in the fic if I choose to continue it but let's see where this goes.**

 **Feedback will be greatly appreciated.**

When Cass Hamada was suddenly tasked with raising the two kids of her late brother, she had expected it to be one of the hardest things to do in her life.

Without any experience to guide her, she had found herself looking through internet sources and asking for advice from friends on how to raise Tadashi and Hiro. During the first few months, she found herself applying some of the text book advices she had read about. She encouraged them to talk about their feelings during mealtimes. She brought them on picnics to nearby parks and organized family game nights or play dates for the two. Heck, she had even set up a bank account called 'for college' for the two boys.

To her surprise though, raising them was easier than she expected. Tadashi, the older one, was more of a caretaker than a child. She had to note that he had grown too fast for his own good. Having his parents die at such an age where he was too old to have not remembered them, yet too young to be taking care of himself and his brother had done a number on his psyche. Before she even noticed it, he had already taken the role of the secondary caretaker in the house. When not in school or working on his robotics hobby, he would help out around the cafe, learn to cook or clean or take the time to teach his little brother something new.

It was a year after she had taken the boys in did she also find out that the younger boy was not your average child as well. At his young age, he was able to figure out in seconds how to assemble the robots his thirteen year old brother was having trouble with. She caught on soon that Hiro Hamada was a once every hundred years prodigy and genius. By thirteen, he had already finished high school, earned thousands of dollars through bot fighting and was well on his way to studying in the same prestigious institute as his older brother.

Then the 'accident' happened. Tadashi, her son, Hiro's brother, her fellow caretaker was gone and she had found herself facing the daunting task of raising a prepubescent and depressed Hiro on her own.

The first few months were hard on the both of them. Cass had wanted to mourn on her own for a few days but with how Hiro had taken it, she knew she had to be the one to stay strong, to hold on to Hiro so he wouldn't fall further into the pit of depression. She continued on with her daily life, attended to her customers in the café, took the calls and replied to messages of condolence from family and friends. Every now and then, she would make conversation with the young boy as she brought food for him from the café. He never replied and the food always remained untouched.

One day, he finally went down the stairs and hurriedly left for school and for Cass, that was a miracle. From that moment, his progress was outstanding. He started studying in the institute, he would go home to tell her about his days in school and she also found out that he has been hanging out with Tadashi's friends. Finally, things were back to normal or at least, as normal as they could ever be.

It was when she was cleaning and accidentally stubbed her two did she discover one of Hiro's big projects. It was this white marshmallow looking robot named Baymax who had 'diagnosed' her stubbed toe and sprayed some medicine on the affected area.

"Who are you?" She had asked.

"I am Baymax, your personal healthcare assistant." It had answered.

"Who made you?"

"Initial programming was done by Tadashi Hamada but all further updates are done by Hiro Hamada."

"When were you made?" Cass had raised her eyebrows in thought. Tadashi had been dead for three weeks yet she had only ever noticed that robot then.

"Tadashi brought me to life on December 5 2014 and Hiro made his first update on April 20, 2015."

 _A few weeks after Tadashi's death_. And it was around that time that Hiro started going to school, eating, talking and most importantly, recovering.

Cass had put two and two together and figured out that a huge chunk of Hiro's recovery was attributed to Tadashi's memory which existed inside Baymax. She had kept much of her knowledge about Baymax to herself until eventually Hiro started becoming more open about his involvement in keeping Tadashi's memory alive with that robot.

Cass was relieved to know that Hiro was learning to move on. He had gotten a scholarship grant at SFIT, his grades were great and he had a promising future yet, she could not shake the feeling that something was wrong with her nephew.

It was not an easy thing to notice at first.

During his freshman year, Hiro only had one major project and that was upgrading Baymax by installing a fighting chip to the robot, adding a "protection" program to the "healing" one. That got him an A plus for sheer mastery of the programming skill. With that, he was able to move on to second year and that's when Cass started to notice it.

Hiro's major project in sophomore year was to expand the repertoire of Baymax by adding more illnesses and symptoms to the already wide repertoire of the robot, giving him the ability to accurately diagnose most illnesses, excluding a few rare ones. By the end of that year, Baymax was capable of diagnosing almost everything from a common cold or an abrasion to much more serious diseases like cancer or a congenital heart disease. There was no explanation needed for the A plus Hiro had gotten for that year.

Junior year was to be his last year in SFIT. He was given a study grant for further studies by the government and Aunt Cass knew that many companies were eagerly waiting for the day the young prodigy would graduate yet she couldn't help but notice that instead of looking excited, Hiro looked miserable.

 _Not necessarily miserable…_ She had to rephrase that. _He_ _ **was**_ _enjoying himself._ She just noticed that there was no passion in his eyes anymore as he sketched plans and did repairs and upgrades. It was as if he were forced to.

She knew enough about SFIT to know that they never really limited anyone to a certain kind of project. They encouraged creative thinking and resourcefulness thus, most projects were what the student wanted to do, not what they were forced to do. Yet, Hiro didn't look like he was enjoying robotics anymore.

One night in the kitchen, she found herself looking closely at her nephew who was sketching some designs in his notebook through bites of dinner.

"So, what's your major project this year?" She asked, an attempt at conversation.

"I'm thinking of either upgrading the repertoire of Baymax to add diagnosis of rarer diseases or to add basic treatment of more serious illnesses like cancer or diabetes… Or… I could do both I guess?"

"Have you considered making your own robot instead of upgrading Tadashi's robot _every year?_ "

Hiro looked at his aunt with a confused expression. "This was what Tadashi would have wanted you know…"

Cass flinched, if she continued that conversation, she would probably be digging her own grave. She instead chose to digress.

"So, what are your plans for further studies? Any certain tracks in mind?"

"I was planning on going for Medical Technology or Biotechnology."

"Why? I didn't expect you to be the type, Hiro."

Hiro frowned. "Well it would be easier to upgrade Baymax that way and besides, that's what Tadashi planned on getting."

Cass had to use all her willpower to stop herself from slapping her forehead where she stood. _This was the problem. Hiro has lost all sense of individuality._ She started to realize that the person in front of her was no longer Hiro Hamada but a younger version of Tadashi without the passion or drive.

"You think you'll enjoy it?" Cass asked. "I mean you've never looked like the type to do that kind of research until now."

"I thought about this Aunt Cass…"

"You should be doing something you enjoy, something you have passion for, something you'd strive hard for. I mean, are you sure _this_ is the right path. What if you take a gap year? Think it through?"

Hiro sighed and narrowed his eyes at his aunt. "I know what I want.. Tadashi would have taken that track, so I will."

Cass found herself taken aback by the blatant stupidity of what Hiro just said. " _Tadashi is…. "_ She started, she was about to say that taboo word but stopped herself when she saw Hiro's hurt expression. " _not here anymore."_

"Thanks for the reminder, Aunt Cass. I'll just go to bed now and reflect on that." Hiro said, his voice laced with sarcasm. He stood up and was about to make his way back to his room.

"Wait, Hiro…" Cass started as she put her hand on his shoulder. "What I'm trying to say is, _you're not Tadashi Hamada. You're Hiro Hamada_. So, when you make choices as big as what to do for the rest of your life, you don't think about what Tadashi wants, you think about what _you_ want."

"What if what I want is to do what Tadashi wanted to do?" Hiro had answered back with a question yet at the same with a tone that said 'end of conversation' and Cass had found herself speechless as she watched Hiro shrug off her hand and make his way up the stairs.

"Urghhh!" Cass wanted to pull all her hair out. _That boy was frustrating!_ She felt like banging her head against the wall, getting some pans, bang it on his head and on her own.

 _Okay, calm down Cass…_ She told herself again and again like a mantra. She put away the dishes and went back to her room, carrying a sleepy Mochi with her. She looked around the room, deep in thought when her eyes rested on the big jar in the corner.

'For College' It said.

She had collected a percentage of her earnings every year so she would be able to secure good lives for both her nephews but with Tadashi gone and Hiro on scholarship, she realize that the money in the jar wasn't really needed anymore. There was a lot of money inside that jar though. She could book a trip around the world or buy a new sports car but when she focused on the label which said 'for college', she started to feel guilty for even thinking about it.

She looked back at Hiro though and realized even if his future _is_ secure, it didn't mean he was going to be happy. She had to find a way to change that. She then made a promise to herself. _That money can only be spent on bettering Hiro's future._

 _And she knew where to start._

 **I actually started this and another Big Hero six fanfic hahah. I don't know what to focus as of the moment but who knows?**

 **What do you think? :D Do tell me!**


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